Infiniband (IB) architecture developed by the Infiniband Trade Association (IBTA) defines a System Area Network (SAN) for interconnecting processor nodes and input/output (I/O) nodes through an IB fabric made of cascaded switches. Each IB node or switch may attach to a single or multiple switches or directly to another IB node or switch. An IB node connects to the fabric via a host channel adapter. Two or more IB subnets may be interconnected by one or more IB routers.
An IB endpoint may be identified by a queue pair number (QPN) and a port identifier. The latter may include a local identifier (LID) and a global identifier (GID). A LID is a 16-bit value that may be assigned when the corresponding port becomes active. A GID is a 128-bit value that may be formed by concatenating a 64-bit IB subnet prefix and a 64-bit GUID (Global Unique Identifier). Both GID and LID may be assigned by a subnet manager, which is a component performing configuration and control of the subnet.
IB architecture supports several methods of data transfer, also referred to as IB transports, including unreliable datagram, reliable datagram, reliable connected, and unreliable connected. Unreliable datagram mode is universally supported by all IB nodes, and hence is used for Internet Protocol over Infiniband (IPoIB) implementation defined in RFC-4391 and RFC-4392 by Internet Engineering Task Force (IETF). Reliable connected and unreliable connected are commonly referred to as Infiniband Connected Mode (CM). The latter mode may also be used for IPoIB implementation, as defined in RFC-4755.